In many urban areas, the sounds of vehicle horns and emergency vehicle sirens are common place. While these horns and sirens serve an important purpose, they also create noise pollution, a known contributor to deleterious cardiovascular effects in humans. In many developed areas, residences and businesses are located above busy traffic areas, a situation in which surrounding infrastructure effectively amplifies the sound reaching these residences and exacerbates noise pollution problems. Additionally, many sirens utilize simple acoustic horns in order to amplify their sound level—horns which have directional properties that are not optimized for their intended use. For example, the main purpose of emergency vehicle sirens is to alert vehicles on the street ahead of the emergency vehicle, and on adjoining side-streets, so that those vehicles will yield the right-of-way. However, these sirens do not focus their transmitted acoustic energy at ground level, and can often be clearly heard on the upper floors of office buildings or residences, where the sound they produce does not serve a useful purpose. In addition, the reflections of the sound waves often make it difficult for other drivers to determine the location of the emergency vehicle.
What is needed to solve the problem of reducing noise pollution resulting from sirens and other acoustic sources is a device that targets its acoustic energy only in the directions needed. A siren with a three-dimensional sound radiation pattern (wide horizontal beam pattern angle and narrow vertical beam pattern angle), so that the siren can be heard ahead and to the sides of the vehicle, but is strongly attenuated in the vertical direction, accomplishes this objective.